Low-level lead exposure, executive functioning, and learning in early childhood.

The current paper presents evidence relating low-level lead exposure to impaired executive functioning in young children. Using the Shape School task, we assessed focused attention, attention switching, working memory, and the ability to inhibit automatic responses in a cohort of 170 children. Participants performed the Shape School task at both 48 and 54 months of age; the mean blood lead level was 6.49 microg/dl at 48 months. After controlling for a wide range of sociodemographic, prenatal, and perinatal variables, blood lead level was negatively associated with children's focused attention while performing the tasks, efficiency at naming colors, and inhibition of automatic responding. In addition, children with higher blood lead levels completed fewer phases of the task and knew fewer color and shape names. There was no association between blood lead and performance on the most difficult tasks, those requiring attention switching or the combination of inhibition and switching. Children's IQ scores were strongly associated with blood lead and Shape School performance, and when entered as a covariate, only color knowledge and the number of tasks completed remained significant. Results provide only weak support for impaired executive functioning, but the deficits in color knowledge may indicate a primary sensory deficit or difficulty with forming conditional associations, both implicating disruptions in dopamine system function.